BAGRAM AIR FIELD, Afghanistan — The Sept. 11 attacks were both a tragedy and a call to arms for many of the soldiers at this sprawling military air base — although few would have guessed that eight years on, the war in Afghanistan would still be raging.

Many of the troops now fighting here were high school students at the time. Some saw the attacks on TV during class, and vowed to sign up when they were old enough.

Army Sgt. Joshua Applegate of Springfield, Miss., was in high school when the planes hit the towers, and enlisted two years later, though he said he had wanted to do it right away.

"I like my country too much not to," said Applegate, who arrived in Afghanistan in April and now facilitates transport and other logistics at Bagram Air Field, the main U.S. base in the country, located just north of the capital, Kabul.

It's nearly eight years since U.S. forces invaded to oust the Taliban and hunt for al-Qaida leaders, including Osama bin Laden, who remains at large. Now soldiers like Applegate are fighting a war that is shifting its focus amid waning public support.

Many troops called Friday's anniversary a galvanizing event, and said marking the day reminds them that the U.S. mission here is important.

"It's still one of the reasons why we're here. September 11 is part of it. For those of us who see the repercussions of fighting, it's still there every day," said Air Force Capt. Christopher Dupuis, 26, of Lacey, Wash.

The remembrances started at dawn Friday, with Dupuis and more than 1,000 other service members donning shorts and sneakers to run exactly 9.11 kilometers (about 5.5 miles) to commemorate the day and remember troops who have died in the fighting since.

At 5:16 p.m. Thursday, the time in Afghanistan when the first of two planes hit the World Trade Center in New York City, a ceremony began at Bagram with an officer reading a minute-by-minute timeline of events on that day. The base's flag fluttered at half-staff as 200 soldiers and other military personnel sang "America the Beautiful" and the national anthem as the sun set.

A changed operationThe anniversary may bring back memories, but the war's mounting casualties are a reminder of how much has changed. Afghanistan is no longer an operation of targeted strikes to rout the Taliban and ferret out al-Qaida leaders. It is an all-out effort, with more than 21,000 troops added this year by President Barack Obama and potentially more to come.

The added forces have meant more contact with the enemy. August was the deadliest month for U.S. troops so far, with 51 killed. And 2009 has been the deadliest year of the conflict for American forces. Since the invasion, at least 747 members of the U.S. military have died in Afghanistan and the region, according to figures from the Defense Department.

The U.S. and its allies invaded Afghanistan in October 2001 to oust the Taliban regime for sheltering al-Qaida leaders who planned the Sept. 11 attacks on New York and Washington.

The Taliban were quickly routed, but the militants regrouped and have mounted an increasingly strong insurgency over the past three years that threatens Afghanistan's struggling democracy.

Soldiers at Bagram said their mission has grown beyond those autumn days of 2001 when priority No. 1 was to get bin Laden.

"It's more about establishing Afghanistan's government and the freedom of the Afghan people," said Army Capt. Jeremy McHugh, 38, of Petersham, Mass. He says he's still fighting terrorism, though indirectly.

As soldiers snacked on oranges and sports drinks at the base, they talked about getting medical supplies out to nearby villages or training Afghan counterparts or improving the government.

It's unclear if bin Laden is even in Afghanistan — many suspect he could be hiding in the tribal regions of neighboring Pakistan — and few of the soldiers say they'll be ready to declare "mission accomplished" even if he's caught.

‘A lot of people have forgotten’Recent opinion polls in the U.S. suggest Americans may be tiring of a conflict that some say is unwinnable and now seems far removed from the effort to find bin Laden.

In mid-July, an AP poll indicated that 53 percent of Americans opposed the Afghanistan war and 44 percent supported it. In August, an ABC News-Washington Post poll found that 51 percent said the war was not worth fighting, while 47 percent said it was worth it.

"I feel that a lot of people have forgotten. I would have them replay the video from that day," said Air Force Technical Sgt. Shawn Merchant, 33, of Ellsworth, Maine.

Merchant, who helps maintain fighter planes at Bagram, just started his second tour in Afghanistan. He says he sees some changes since 2007: Everything at Bagram is bigger and more permanent.

Meanwhile, the planes are dropping fewer bombs. Directives issued by the top U.S. commander in Afghanistan have called for more caution with air strikes. Recent strikes that have killed civilians have been used as propaganda tools by Taliban militants.

Back in 2001, Merchant was stationed in Alaska and watched footage of the planes hitting the World Trade Center on base.

"It became what Pearl Harbor was in World War II: Now we step up," Merchant said.

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